Huh? There’s no shortage of compatibility layers and cross-platform applications. Outside of mobile devices it’s more like the norm.

Operating system compatibility layers: WINE, Windows Subsystem for Linux, Linuxulator.

Cross-platform runtimes: JVM, Mono, Electron.

Cross-platform applications: Firefox, Chrome, Oracle DB, Postgres, MySQL, Apache, nginx, etc.

Multi-OS software repositories: Homebrew, Steam, Epic, etc.

Clouds even host FOSS-as-a-service.